Applying Phosphorous Cross-Polarization/Magnetization Transfer to Probe the Membrane/Water Interface in Myelin

Motivation: Most current MRI methods to study myelin rely solely on 1H nuclei. Because 1H is ubiquitous, this limits the specificity and detail of the information these methods can provide. Goal(s): To develop a suite of information-rich techniques, based on a new combination of 31P cross-polarization with magnetization transfer, that are specific to lipid membrane/water interfaces. Approach: We developed a family of pulse sequences that transfer membrane 31P magnetization to water (1Haq) to make relaxation and indirect spectroscopy measurements. Results: These new sequences provide 1Haq-detected wideline semi-solid 1H (1Hs) and 31P NMR spectra and relaxation data, specific to the membrane/water interface in myelin. Impact: Detecting membrane-specific 31P and 1Hs NMR signals through MRI-visible 1Haq could provide new and extremely specific MRI contrast mechanisms for myelin, providing superior sensitivity to membrane condition than existing proton-only metrics.